Recently, specifications for wireless Internet service standard were introduced by the international standardization organizations such as BRAN HIPERLAN/2, IEEE 802.11a and IEEE 80216. Accordingly, related systems for wireless Internet service have been actively developed. There are also many studies in actively progress to develop a packet transmission technology to prior occupy a technology for the fourth generation of packet based mobile telecommunication system.
In the packet transmission technology, a packet scheduling scheme is introduced to maximize the efficiency of wireless resource for transmitting packets. The packet scheduling scheme has been specialized as a field of sharing wireless link and is used as a method of improve the capacity of system compared to a conventional line mode.
The real-time traffic must obey delay requirement conditions due to its characteristics and a predetermined level of packet loss rate must be guaranteed. A quality of service (QoS) is suggestively guaranteed when the real-time traffic is transmitted if a call is accepted through a call connection control in a typical line mode including a code division multiple access (CDMA) dedicated channel. Therefore, a dedicated scheduler is essential to satisfy QoS such as delay in the packet mode. Since the wireless environment is dynamically changed in a time domain differently from the wired environment, such a characteristic must be reflected into the scheduling algorithm.
A packet scheduler for real-time traffic services session having a longer delay in a buffer first of all. In this case, there is large possibility that the scheduler cannot satisfy the absolute delay requirement conditions although the scheduler minimizes the delay. When the scheduler selects a session to be transmitted from a current slot to a next slot, the scheduler has a difficulty to reflect a packet lost rate caused by the delay because the scheduler reflects only a delay state of a head of line (HOL) packet which arrives at the buffer at first.
In order to describe a conventional scheduler, there are assumptions as follows. There are two sessions A and B. A HOL delay of the session A is 50 ms and a HOL delay of the session B is 100 ms. And, same number of packets for the sessions A and B are stored in each buffer. Furthermore, the number of packets of the session A are not be deleted is 10 if those are not transmitted in the next slot, and the number of packets of the session B are not be deleted is 1 if those are not transmitted in the next slot.
Under such assumptions, if the packets are scheduled to transmit by only considering the simple delay and the number of packets in the buffer, the session B will be selected. If the wireless channel conditions of two sessions are identical and a current slot can transmit five packets, the session A may transmit four packets which are not required to transmit at the next slot. Then, the session B may loss a chance to sent 10 packets to transmit with the next slot. If the session A is selected, the five packets will be transmitted and five packets will be deleted. Therefore, it is better in the view of QoS to select the session A than to select the session B.